Shotgun pellet that is elongated, achieves stable flight after disordered launching, and is easy of manufacture

ABSTRACT

A shotgun pellet that flies faster and farther for a given pellet weight than spherical pellets or other shapes by means of streamlined aerodynamic design, having no features that fail to transit the barrel without damage, orienting itself nose-into-the-wind despite disordered launching, spins about its axis, minimizes or eliminates nutation, and is manufactureable in a coaxial two-element die and punch cold-forming machine.

FIELD OF THE INVENTION

This invention relates to elongated, streamlined shot pellets that exhibit improved flight characteristics, are economical to manufacture, and can be made of various materials.

DESCRIPTION OF PRIOR ART

Non-spherical shot pellets have received attention in recent years due to the aerodynamic inefficiency of the historical sphere, but they have failed to achieve stable, efficient flight combined with low cost of manufacture.

Spherical lead shot pellets have been in use since the early days of shotgunning due to the abundance and low cost of lead, its high density and the ease with which round lead pellets can be manufactured in a shot tower. Those features have caused lead shot pellet usage to endure to the present where the use of lead remains permissible.

Recent years have seen lead shot fall into some disfavor due to the toxicity of lead, and though non-lead pellets have been developed they have not extensively displaced lead. Those with densities in the range of the density of lead are too costly to gain a significant market share, and lower density spherical steel shot, which is the least costly of the various nontoxic shot available, has dominated the nontoxic shot market. Governmental mandate now requires nontoxic shot in several applications, so steel shot dominates in those applications since steel is available that is of low cost and is soft enough to be readily formed. The lower density of steel has been partially compensated by industry changing to shotguns that endure higher chamber pressures, which create higher muzzle velocities. The ammunition industry now manufactures considerable volumes of spherical steel shot.

References Cited U.S. Pat. No. 3,650,213 March 1972 Abbott U.S. Pat. No. 3,880,083 April 1975 Wasserman U.S. Pat. No. 4,718,348 January 1988 Ferrigno U.S. Pat. No. 5,279,787 January 1994 Oltrogge U.S. Pat. No. 6,439,126 August 2002 Kennedy

Abbott presents a tear-drop shaped projectile with tail fins, Wasserman a projectile with materials of differing densities to obtain a forward center of gravity, Ferrigno a tear-drop shaped projectile with a sharp tip of tail and curved nose grooves for rotation, Oltrogge shows an unclaimed tear-drop shape either with or without tailfins, and Kennedy a tear-drop shaped projectile of materials of differing density and flying with the small end forward, somewhat like a badminton birdie.

Spherical shot sheds vortices alternately from one side of the pellet then the other, which is called a von Karmen Vortex Trail, or Vortex Street. The vortices are high-energy phenomena that obtain their energy from the shot pellet, thereby reducing its range and partly explaining why a sphere has poor aerodynamic efficiency and an erratic flight path compared to a streamlined pellet. Additionally, a sphere travels in a curve if it flies with spin, as seen in examples of spin imparted to tennis balls, golf balls and baseballs. Without spin a sphere's flight is erratic, like baseball's knuckleball. Hence the interest in more streamlined shapes for shot pellets that enable them to fly faster and farther.

Various forms of teardrop-shaped and elongated pellets are shown in the cited references, and are correctly presented as offering reduced drag when they fly with the pellet geometric axis coincident with the pellet vector and the pointed tail on the trailing end. However, a teardrop pellet without tail fins is unstable and can rotate in flight, resulting in poorer aerodynamic performance than a sphere.

The references cited include teardrop pellets that have fins on the tail to increase the weathervaning effect to the level of preventing continuous spin about an axis other than the pellet geometric axis. Such fins have proven fragile and do not well survive transit of the shotgun barrel. If other means are supplied to provide pellet spin about its geometric axis, the tail fins resist such spin. If the tail fins are placed at an angle, to provide pellet spin about its own axis, they too are fragile and tend to force a nutating rotation due to unsymmetrical damage to the fins. Such pellets are also more complex to manufacture. Teardrop pellets have been suggested with means in the nose to provide axial spin, but those means are ineffective until the pellet is flying nose-first into the wind, which does not occur until weathervaning has been effected. The latter is effected with tail fins, requiring the nose means to overcome tail fins that resist pellet rotation, or if the tail fins are angled, the nose means are redundant.

One reference stacks teardrop pellets nose-to-tail in the shotshell case to launch them nose-first into the wind, which is economically defeating while also unduly limiting the number of pellets in the shell casing. Various other shot pellets have been proposed but none that is streamlined, has fins or other means that accomplish weathervaning that survive transit of the shotgun barrel, are nontoxic, and also economical of manufacture.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1.

An example of claimed shot pellet shape.

FIG. 2

Shows the pellet launched laterally into the wind with resultant net clockwise moment that turns the pellet nose-first into the wind.

FIG. 3

Five different pellet outlines out of the many that are possible

FIG. 4

Process of the pellet weathervaning when launched other than nose into the wind

FIG. 5

Process of a tear-drop shaped pellet failing to weathervane into the wind

FIG. 6

Detail of a method of creating recessed surfaces in pellet nose to cause pellet rotation about its geometric axis.

FIG. 7

Process whereby a pellet without a cylindrical section in the tail can nutate.

FIG. 8

Process whereby a pellet with a cylindrical section in the tail can avoid nutation

FIG. 9

Punch-and-die sets that cannot make spheres or a smooth transition from a curved surface to a cylindrical surface

FIG. 10

Punch-and-die set that makes a smooth transition from a curved to a cylindrical surface.

DETAILED DESCRIPTION OF THE INVENTION AND THE FIGURES

The present invention is streamlined, can be launched in any attitude, has a center of gravity and an extended tail that combine to cause weathervaning, which is the turning of the pellet to nose-into-the-wind attitude, and effects stability in nose-forward flight. It spins about its axis, can be made of any material that forms in a punch and die, has no protruding fins, enabling survival of barrel transit, is economical of manufacture, requires no secondary manufacturing operations, exhibits low aerodynamic drag, and efficiently fills the space in a shell casing.

Definitions of Digital Identifiers in the Figures:

-   -   11. Pellet center of gravity     -   12. Recessed rotational surface in pellet nose     -   13. Nose-to-tail interface     -   14. Cylindrical portion of nose     -   15. Cylindrical portion of tail     -   16. Boattail     -   17. Wind direction     -   18. Clockwise moment     -   19. Counter-clockwise moment     -   20. A pellet that is oriented into the wind     -   21. Element of the cone that is parallel to the wind direction     -   22. Cone element that is protruding into the wind     -   23. Forming die     -   24. Forming punch     -   25. Formed pellet     -   26. Cylindrical portion of pellet     -   27. Diametral bulge on the formed pellet

FIG. 1 is a profile view of one form of the present invention, with one possible type of recessed nose vanes, and showing two portions of the pellet length that are of cylindrical shape. The nose vanes are omitted from most subsequent figures for clarity, but are shown in FIG. 6 in detail.

FIG. 2 shows the pellet of FIG. 1 launched into the air with its geometric axis at ninety degrees to the pellet vector, the pellet vector and the wind vector being colinear. The lateral drag on the portion of the pellet forward of the center of gravity creates a counterclockwise moment about the center of gravity, and the lateral drag on the pellet aft of the center of gravity creates a clockwise moment about the center of gravity. The countervailing moments are unequal and the longer tail is designed to cause the clockwise moment to prevail and to turn the pellet nose-first into the wind. To keep the center of gravity sufficiently near the forward end of the pellet, since the center of gravity acts as the pivot point, the tail is longer and of smaller diameter than the nose.

FIGS. 3A, B, C, D and E, without limitation, are several depictions of many possible variations of pellet profile. All show a pellet of circular cross-section, which is not a theoretical limitation, although alternative cross-sectional geometries are more costly to manufacture and suffer greater aerodynamic drag. Pellet tail tends to be about twice the length of pellet nose.

FIGS. 4A, B, C and D illustrates a pellet of the present invention just launched into the air from the muzzle of a shotgun with pellet geometric axis at ninety degrees to pellet vector, as in FIG. 2. The weathervaning effect turns it to the position shown in FIG. 4B, but whereas the pellet had no rotational inertia in FIG. 4A, it does have rotational inertia in FIG. 4B about an axis other than the pellet geometric axis and it moves to approximately the position shown in FIG. 4C, where the rotational inertia is overcome by the weathervaning effect and the pellet returns to approximately the position of FIG. 4D, demonstrating damping of pellet oscillation.

FIGS. 5A, B, C and D show how a teardrop pellet, and others of inadequate lateral tail drag, in the position of FIG. 5A continues its clockwise rotation to positions 5B, C and D, lacking sufficient weathervaning effect to change rotation to counterclockwise when in position 5C. When in position 5D the weathervaning effect abets the clockwise rotation that is in progress. The pellet with inadequate lateral tail drag flies on through the air continuing to spin in this manner, i.e., about an axis other than the pellet geometric axis, and exhibits higher aerodynamic drag than a sphere. This is a common effect that is widely seen, often in a ricochet. FIGS. 5A through 5D illustrate how many pellets, and especially those without tail fins, do not have adequate weathervaning effect to settle them into nose-forward flight.

FIG. 6 shows a simple recessed surface in the pellet nose that is easy of manufacture and provides spin of the pellet around its geometric axis when traveling nose-forward. The present invention has no tail fins in order to avoid the damage that fins suffer while transiting the barrel. The present means, without limitation, are shown in FIG. 6 and are in the form of planar recessed surfaces in the pellet nose that use impinging air to impart a spinning motion about the pellet geometric axis. The recessed surfaces well endure barrel transit, and, by being planar or nearly so, they avoid the costly manufacturing techniques required by protruding fins, or by the curved grooves of U.S. Pat. No. 4,718,348. There must be at least two such surfaces in order to accomplish symmetric torque about the pellet geometric axis. FIG. 6C includes a section view as indicated.

Recessed vanes can be made in a conical nose by use of a hyperbola on the cone that is created by a plane passed through the cone parallel to the cone axis. The straight line, or its alternative, created by the intersection of the two said planar surfaces has each terminus located on said hyperbola, one on each branch of the hyperbola with one further from pellet nose than the other.

Pellets with a tail similar to that of FIG. 1 but without the cylindrical section, and having rotational means similar to that of FIG. 6, may achieve a limited degree of stability by means of rotation about the pellet geometric axis. But they usually experience nutation, which is the tip of the pellet tail continuously moving in a circle during flight, as viewed in the direction of the pellet geometric axis. The present invention also includes a method to further stabilize the pellet by diminishing or eliminating nutation. The method is to make the tip of the pellet tail cylindrical. Some such pellets are shown, without limitation, in FIGS. 5 and 7. FIGS. 7 and 8 illustrate how nutation is suppressed by the cylindrical section of the tail protruding into the slipstream to create a corrective force on the pellet.

FIGS. 7A, B, C and D illustrate why nutation can be of greater magnitude in pellets with no cylindrical section at the tip of the tail. FIG. 7A shows a pellet without a cylindrical tail tip flying straight ahead and having a tail cone included angle of 20 degrees. FIGS. 7B and C illustrate how the pellet axis of symmetry of those pellets can deviate within an arc of 20 degrees, or whatever the included angle of the tail may be, with no protrusion of the pellet tail into the slipstream. The side of the tail cone that is parallel to the pellet vector does not protrude into the slip stream. In three dimensions, the pellet tail is free to move within 10 degrees in any direction from the pellet vector, and nutation results. FIG. 7D illustrates that the pellet axis must deviate from pellet vector by more than half the tail cone included angle to cause the tail cone to protrude into the slip stream, like an airplane rudder, to accomplish straightening of the plane.

FIGS. 8A, B, C and D depict a pellet with a cylindrical tip of tail in circumstance parallel to the FIG. 7 with the same letter designation. FIGS. 7A and 8A show the pellets moving straight ahead. In FIGS. 7B and 8B the out-most tail cone elements are parallel as shown, and are also parallel to the wind vector. That circumstance also obtains in FIGS. 7C and 8C but to the opposite side. However, when the pellet axes of FIGS. 8B and C digress the same amount as those in FIGS. 7B and C, the cylindrical elements of FIGS. 8B and C protrude into the slip stream and a directionally corrective force is created. As illustrated in FIG. 8D, when the pellet with the cylindrical tip deviates just a very small amount from straight ahead, the cylindrical tip protrudes into the slip stream and a corrective force occurs, and nutation is minimized or eliminated. The pellet of FIG. 7D must turn to a much larger angle than the pellet of FIG. 8D to move its tail-tip to the same angle as the cylindrical tip of FIG. 8D.

The cylindrical tip may be other than cylindrical, such as, without limitation, triangular, square, pentagonal or other as long as that section is axisymmetric geometrically and inertially. The tail may be shaped like the tail of a badminton birdie, so as to provide an enhanced corrective to nutation, at the cost of increased aerodynamic drag in straight-ahead pellet flight. All such shapes increase cost of manufacture, exhibit higher straight ahead drag and are not as volumetrically efficient of shell casing space. A traditional boattail can be added to advantage to the tail tip of any pellet herein disclosed to reduce aerodynamic drag. All pellets of this invention can also be made to include a tail that is cylindrical, or nearly cylindrical, as a major portion of the length of the tail as shown in FIG. 3.

The above pellets are shown with a tail section of smaller diameter than the nose section. A pellet could be made with a tail of the same diameter as the largest diameter of the nose, but with the tail being hollow to achieve the needed forward location of the center of gravity. However, in order to keep the center of gravity well forward and thereby to obtain sufficient weathervaning effect, the wall of the hollow tail must be so thin as to render it unable to withstand barrel transit without damage. A hollow tail can be used if tail diameter is sufficiently reduced to obtain adequately forward center of gravity, and adequate wall thickness of the tail, but complexity and cost of manufacture escalate. Also, volumetric efficiency of the shot charge is diminished.

FIGS. 9A and B reveal how manufacture of the pellets of this invention is aided by avoiding some traditional difficulties of manufacturing spherical pellets. It is seen in FIG. 9A how a simple punch-and-die set requires a knife-edge on the punch in order to form a sphere, requiring the knife-edge to stop at precisely the diametral point in the die on every cycle. FIG. 9B shows a punch-and-die set that avoids the knife-edge, but creates a sphere with a protruding diametral ring that must be removed by a subsequent manufacturing step. There are others, some of which were used for many years.

FIG. 10 shows that the pellets of this invention can be formed by a punch-and-die set that moves on a single line of action, because of the location of cylindrical portions, combined with all other surfaces being tapered away from the nose-tail interface. There is no clocking requirement of punch to die. The short cylindrical pellet section at the point of maximum pellet diameter, at the aft end of the pellet nose in all pellets of this invention, prevents formation of a waist band around the pellet at the point of maximum diameter and obviates the need for a knife-edge on the punch. The present disclosure allows the pellet to be formed with the length of pellet-nose cylindrical section being the variable that compensates for imperfect volumetric constancy of the material pieces that are fed into the die. The result is a very slight variation in the length of the pellets, and without any surface irregularity to require additional manufacturing steps. That is accomplished with force limitation means in the press, such as, without limitation, a spring between the punch and the punch ram, which is common practice. It is seen that an angle on the tip of the punch somewhat other than ninety degrees could be used without becoming a knife-edge. This invention makes no claim to the manufacturing process, but only claims an elongated pellet with the features herein described that is designed so that the simple manufacturing process described can be used.

The recessed rotational surfaces in the nose of the pellet must be inversely replicated in the bottom of the die, which is easily done with an electrostatic-discharge-machining sinker in the shape of the pellet nose.

The design parameters for the present invention are variables. Items, without limitation, such as pellet diameter along various segments of its length, axial length of the various pellet portions, the shape of those portions, and the density of the material of construction all affect, without limitation, the lateral and longitudinal drag coefficients, and the rotational inertia values both longitudinal and lateral. Since the variables have independent effects, a design that works well for a particular circumstance usually cannot, for example, be simply enlarged or reduced in scale to obtain a functional design for a pellet that may have different geometric proportions or a different material density.

The result of this invention is a pellet of unusually high aerodynamic performance that can be dump-loaded into the shell casing because it self-aligns in the wind, has high volumetric efficiency within the shell casing, exhibits limited or no nutation, rotates about its geometric axis, well endures barrel transit, and can be made of low cost material or exotic material, and that is manufacturable by a low-cost process. 

I claim:
 1. A non-spherical shotgun pellet that is elongated and axisymmetric, consisting of nose and tail sections, the nose being shorter than and of greater maximum diameter than the tail, center of gravity being on pellet axis at or near the nose-tail interface, the rear-most section of the nose being cylindrical, all pellet cross-sections being circular except for small cut-outs in the nose where recessed cut-outs occur for rotational purpose, all pellet diameters of the nose and tail are either constant or diminishing with distance from the nose-tail interface, lateral aerodynamic drag of the tail being sufficiently greater than lateral aerodynamic drag of the nose to create a net moment about the center of gravity that rotates the pellet nose-first into the wind when pellet is launched in a different attitude and maintains nose-first attitude throughout flight.
 2. The pellet of claim 1 with a cylindrical section at the tip of the tail which is of a length at least equal to the radius of that cylindrical section, with no protuberance, such as, without limitation, a fin-like protuberance.
 3. The pellet of claim 1 whose nose forward of said cylindrical section is, without limitation, hemispherical, or hemiellipsoidal, or conical with rounded corners, or combinations or variations of said geometries, each being or nearly being tangent to said aft cylindrical portion of pellet nose.
 4. The pellet of claim 1 with at least two recesses in the nose, each recess consisting of two planar surfaces at right angles to one another, one plane being parallel to pellet axis and the other plane being at an angle to pellet axis such that air impinges it when pellet is nose-first into the wind.
 5. The pellet of claim 1 with the recesses of claim 4 being faired smoothly to adjoining surfaces.
 6. The pellet of claim 1 with the planes of claim 4 being at other than right angles to one another.
 7. The pellet of claim 1 with the planes of claim 4 being nonplanar.
 8. The pellet of claim 1 with aft end of nose being an annulus that is perpendicular to pellet axis with an outer radius that is the same as the radius of said cylindrical aft end of pellet nose, and an inner radius that is the length of the radius of the tail where it joins the nose.
 9. The pellet of claim 1 with annular ring of claim 6 being nonplanar.
 10. The pellet of claim 1 with tip of tail chamfered in the manner of a traditional boattail.
 11. The pellet of claim 1 with a tail that terminates with the cylindrical section of claim 2 and includes the boattail of claim
 10. 12. The pellet of claim 1 which is of minutely variable length due to variations in the length of said cylindrical section at the aft end of pellet nose caused by imperfect consistency of size of blanks that are fed into the manufacturing device. 